A malocclusion is a misalignment of teeth or incorrect relation between the teeth of the two dental arches. The term was coined by Edward Angle, the “father of modern orthodontics,” as a derivative of occlusion, which refers to the way opposing teeth meet. Angle based his classifications of malocclusions on the relative position of the maxillary first molar. According to Angle, the mesiobuccal cusp of the upper first molar should align with the buccal groove of the mandibular first molar. The teeth should all fit on a line of occlusion, which is a smooth curve through the central fossae and cingulum of the upper canines, and through the buccal cusp and incisal edges of the mandible. Any variation therefrom results in malocclusion.
There are three classes of malocclusions, Class I, II, and III. Further, class II is subdivided into three subtypes:
Class I: Neutrocclusion Here the molar relationship of the occlusion is normal or as described for the maxillary first molar, but the other teeth have problems like spacing, crowding, over or under eruption, etc.
Class II: Distocclusion (retrognathism, overjet) In this situation, the upper molars are placed not in the mesiobuccal groove, but anteriorly to it. Usually the mesiobuccal cusp rests in between the first mandibular molars and second premolars. There are two subtypes:
Class II Division 1: The molar relationships are like that of Class II and the anterior teeth are protruded.
Class II Division 2: The molar relationships are class II but the central incisors are retroclined and the lateral incisors are seen overlapping the central incisors.
Class III: Mesiocclusion (prognathism, negative overjet) In this case the upper molars are placed not in the mesiobuccal groove, but posteriorly to it. The mesiobuccal cusp of the maxillary first molar lies posteriorly to the mesiobuccal groove of the mandibular first molar. This malocclusion is usually seen when the lower front teeth are more prominent than the upper front teeth. In such cases, the patient very often has either a large mandible or a short maxillary bone.
Orthodontics, formerly orthodontia (from Greek orthos “straight or proper or perfect”; and odous “tooth”), is the specialty concerned with the study and treatment of malocclusion (improper or dysfunctional bite), which may be a result of tooth irregularity, disproportionate facial skeleton relationship, or both. Orthodontics treats malocclusion through the displacement of teeth via bony remodeling and control and modification of facial growth.
Bone is remodeled by the concerted activities of 3 cell types—osteoblasts, osteocytes, and osteoclasts. Osteoblasts are the cells that produce bone extracellular matrix and are responsible for its mineralization. Osteoblasts also have endocrine activity through secretion of osteocalcin, which regulates fat and energy metabolism. These cells also control the differentiation and activity of osteoclasts. Osteocytes are osteoblasts that have been incorporated into bone matrix and are cells with extensive dendritic processes through which the cells communicate with other osteocytes and with osteoblasts. Mechanical loading is sensitized by the dendritic processes and transferred to biochemical responses involved in control of osteoblast and osteoclast function. Osteocytes also have endocrine activity by releasing fibroblast growth factor 23, which is involved in phosphate secretion in kidneys. Differentiation of osteoclast mononuclear progenitors to mature multinucleated osteoclasts is regulated by macrophage colony-stimulating factor and receptor activator of NF-κB ligand, expressed by stromal cells in bone marrow or osteoblasts in bone, as well as by osteocytes. The integrated endo- and paracrine control of osteoblasts, osteocytes, and osteoclasts is important for maintaining bone mass and for control of remodeling and modeling processes in bone, including during orthodontic-induced tooth movement.
The process of orthodontic bone remodeling has been traditionally accomplished by using a static mechanical force to induce bone remodeling, thereby enabling teeth to move. This widely accepted approach to treating malocclusion takes about twenty-four months on average to complete. In this approach, orthodontic braces, consisting of an archwire that applies a continuous static force and interfaces with brackets that are affixed to each tooth. Braces are used to treat a number of different classifications of clinical malocclusion, including underbites, overbites, cross bites, open bites, and crooked teeth, for both aesthetic and functional/structural reasons.
Orthodontic treatment is complicated by the fact that it is uncomfortable and/or painful for patients, and the orthodontic appliances are perceived as unaesthetic, all of which creates resistance to use. Further, the 24-month average treatment time is very long, and further reduces usage and compliance, which can include chronic poor dental hygiene. In fact, some estimates provide that less than half of the patients who could benefit from such treatment elect to pursue orthodontics.
Kesling introduced the tooth positioning appliance in 1945 as a method of refining the final stage of orthodontic finishing after debanding. A positioner was a one-piece pliable rubber appliance fabricated on the idealized wax set-ups for patients whose basic treatment was complete, but still needed a small amount of refinement. Kesling also predicted that certain major tooth movements could also be accomplished with a series of positioners fabricated from sequential tooth movements on the set-up as the treatment progressed. However, this idea did not become practical until the advent of 3D scanning and computer modeling in 1997.
Removable clear appliances, such as the Invisalign® system, have been introduced for treating malocclusion, and provide greatly improved aesthetics since the devices are transparent. However, because these appliances can be removed, compliance can be an issue, and failure to use slows overall treatment time.
As a treatment modality, aligners are also limited in the classifications of clinical malocclusion that they can address. In the past, aligners have not been able to easily rotate or extrude teeth because the aligner cannot adequately direct force in all directions. Being aware of these limitations, Align Technologies has recently combined the Invisalign® clear aligners with clear attachments that adhere to teeth and can provide a surface on which force can be exerted in any desired direction. A custom mold is made using a 3D model of the patients teeth with pockets therein for the placement of a force attachment, the placement and shape of which are determined using proprietary modeling software. The relevant force attachments are made and fitted into the mold, adhesive applied to the attachments, and the mold applied to the teeth. This allows precise and quick placement of the clear attachments, which are then affixed using light cure. There is some affect on aesthetics, but because the force attachments are also clear, they are not very noticeable from a distance.
In addition to static forces, cyclic forces can also be used for orthodontic remodeling. Kopher and Mao assessed cyclic forces of 5 N peak magnitude at 1 Hz in rabbits, while Peptan and Mao assessed cyclic forces of 1 N at 8 Hz in rabbits, and Vij and Mao assessed cyclic forces of 300 mN at 4 Hz in rats. In aggregate, the data from these three studies indicated that cyclic forces between 1 Hz and 8 Hz, with forces ranging from 0.3 N to 5 N, increased bone remodeling. Rates depended on different methodologies, but increases of 2.5× with vibrational forces were common.
The early Mao studies provided a basis for both possible efficacy and likely safety for using vibration in humans to assist orthodontic tooth movement. However, Mao's early experiments were performed on rabbit cranial suture closure model, and no device was ever built that could be used for human teeth. Thus, although suggestive, the work needed to be repeated on human teeth to prove its efficacy. However, no such device was available.
OrthoAccel® Technologies Inc., invented the first commercially successful dental vibrating device, as described in US20080027046, designed to apply cyclic forces to the dentition for accelerated remodeling purposes. Both intraoral and extraoral embodiments are described in US20080227046, each having processors to capture and transmit patient usage information. The bite plate was specially designed to contact occlusal as well as lingual and/or facial surfaces of the dentition, and thus was more effective than any prior art devices in conveying vibrational forces to the teeth.
Further, the device was tested in human clinical trials and shown to speed orthodontic remodeling as much as 50%. As such, it is truly a breakthrough in orthodontic technology (Kau 2010). Finally, the device is slim, capable of hands free operation, lacks the bulky head gear of the prior art devices, and has optimized force and frequency for orthodontic remodeling. Thus, its comfort level and compliance was also found to be high, with patients reporting that they liked the device, especially after the motor was redesigned to be quieter and smoother, as described in US20100055634 et seq. In fact, this device has been marketed as AcceleDent® in in several countries and has achieved remarkable commercial success since its recent introduction. AcceleDent® represents the first successful clinical approach to accelerate orthodontic tooth movement by modulating bone biology in a non-invasive and non-pharmacological manner.
However, further improvements in the above device are always beneficial, and this application addresses some of those improvements.